Earth Planets Space, Vol. 58 (No. 10), pp. 1333-1339, 2006
Ruben Cejudo Ruiz1, Avto Goguitchaichvili1,2, Silvana E. Geuna3, Luis M. Alva-Valdivia1, Jesus Solé4, and Juan Morales1
1Laboratorio de Paleomagnetismo, Instituto de Geofiíica, UNAM, Ciudad Universitaria s/n, 04510 Mexico D.F.
2Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofisica, UNAM, Coeneo, Michoacán.
3Laboratorio 'Daniel Valencio', Departamento de Ciencias Geologicas, Facultad de Cs. Exactas y Naturales, Pab. 2(1428), Buenos Aires, Argentina.
4Instituto de Geologia, UNAM, Ciudad Universitaria s/n, 04510 Mexico, D.F.
(Received December 6, 2005; Revised March 31, 2006; Accepted April 7, 2006; Online published November 8, 2006)
We present here new paleointensity and geochronology results from Early Cretaceous volcanic rocks of Sierra Chica de Cordoba (Argentina). The new K-Ar isotopic ages of 5 samples range from 136 to 122 Ma. Twenty five samples from 7 individual flows yielded acceptable paleointensity estimates. The mean paleointensity values per flow are ranging from 53.0±1.9 to 25.4±2.6 μT and the corresponding Virtual Dipole Moments (VDMs) are ranging from 9.3±1.3 to 4.6±0.5 (1022 Am2). This corresponds to the mean value of 7.3±1.7×1022 Am2, which is compatible to the present geomagnetic axial dipole. Currently available selected paleointensity data from 80 to 130 Ma suggest that geomagnetic field strength frequently fluctuated before and during the Cretaceous Normal Superchron while the magnetic polarity maintained stable. The mean paleointensities derived from Córdoba lavas agree remarkably well with those obtained from the Paraná Magmatic Province (133-132 Ma). This reinforces the hypothesis about the unreliability of 'Mesozoic Dipole Low'.
Key words: Paleointensity, rock-magnetism, Early Cretaceous, South America.